Axle measuring device and method

ABSTRACT

A device and a method for axle alignment, in which an angle between a wheel of a vehicle and a reference direction is determined, the angle being determined using a transducer, which contains at least one rotation speed sensor. The transducer is set so that it assumes a known position with respect to the reference direction. The angle obtained for the transducer arranged on the wheel of the vehicle is a measure of a trail angle or a camber angle of the wheel.

BACKGROUND INFORMATION

European Patent Application No. 313 563 describes a method and a devicefor wheel position measurement, using a rotating gyroscopic devicesuspended by a universal joint. An angle measurement device is adjustedto the first wheel. The subsequently started rotation of the gyroscopicdevice guarantees that the rotation axis of the gyroscopic device, whichis used as a reference axis, does not change during the subsequentmeasurement procedure. The angle measurement device is mounted on thenext wheel, and the angle formed between the wheel and the referenceaxis is measured. This procedure is repeated for all wheels. Thedifferences in orientation of the other wheels compared to the firstwheel are measured, stored, and subsequently compared to one another inorder to determine the wheel adjustment values. The start-up time of thegyroscopic device used as the reference axis is approximately 15 minutesif a high degree of accuracy is required. As an additional angletransducer required in addition to the gyroscopic device, an incrementalangle transducer measures the angle difference between the initialposition and the measured position.

SUMMARY OF THE INVENTION

The device for axle alignment of a vehicle according to the presentinvention, which allows at least one angle to be determined between awheel of the vehicle and a reference direction, provides that the angleis determined using a transducer having at least one rotation speedsensor, whose output signal is integrated. The use of rotation speedsensors for axle alignment makes it possible to dispense with an exactalignment of the transducers with respect to one another on each wheelof the vehicle. Long setup and adjustment times are avoided. Since eachtransducer used for axle alignment assumes a known relative positionwith respect to the reference direction, which does not depend on thevehicle or the arrangement of another transducer, large axle bases oraxle offsets of the vehicle to be aligned have no importance. Thetransducer can be equally used for passenger cars, trucks, trailers ormultiaxle vehicles. The rotation angles obtained by integration are usedas a measure for a trail angle or camber angle of the vehicle. Therotation angle provides the deviation of the rotation axis coordinatesof the wheel from the reference direction. This angle is used as basicdata for the algorithm used to determine the trail angle or camberangle.

In one exemplary embodiment, one transducer has three rotation speedsensors forming an orthogonal system. Thus the reference direction canbe completely isolated from the vehicle. All information required tocompensate interference caused by translational motion is obtained.

In an exemplary embodiment of the axle alignment method according to thepresent invention, a transducer is provided, which has at least onerotation speed sensor whose output signal is integrated. The transduceris adjusted so that it assumes a known position with respect to areference direction. Subsequently it is mounted on one wheel of thevehicle. The angle formed is a measure of a trail or camber angle of thevehicle wheel. The rotation speed sensor measures the relative positionof the transducer with respect to the reference direction. Thetransducer no longer has to be arranged in a predefined position on thevehicle wheel. Time-consuming adjustment procedures thus becomeunnecessary.

In a particular embodiment, a third step is provided, in which therelative position of the rotation axis coordinates of the wheels withrespect to the reference direction is determined. Angular offsets of thewheel axles that occur with respect to one another provide informationon the correction measures on the axle geometry to be taken.

The particular embodiment of the present invention provides for thecompensation for the earth's rotation during angle measurement,increasing the accuracy of angle measurement. Since the rotation speedsensor measures these interfering quantities continuously at rest, alow-maintenance, self-calibrating system can be created.

In a fourth step of a useful refinement, the transducer is set to thesame position as in the first step. The previous measurement is theninvalid if the angle obtained in the fourth step differs significantlyfrom zero. Interference affecting the measurement can be controlledwithout major expense. This measure contributes to more userfriendlyautomation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an exemplary embodiment of a deviceaccording to the present invention.

FIG. 2 shows a spatial arrangement.

FIG. 3 shows a flow chart of an exemplary embodiment of a methodaccording to the present invention.

DETAILED DESCRIPTION

A transducer 10 is constructed from three rotation speed sensors 11arranged orthogonally to one another. Each of rotation speed sensors 11delivers a rotation speed 13 to a signal processor 12, which convertsthe input signals into angle 14. As shown in FIG. 2, transducer 10assumes a certain position with respect to a reference direction 20. Inspatial proximity to transducer 10, two wheels 15 a, 15 b to be alignedare located. Rotation axis coordinates 21 a, 21 b are assigned to eachwheel 15 a, 15 b; one axis of these coordinates coincides with therotation axis of the respective wheel 15 a, 15 b.

Rotation speed sensors 11 measure rotation speed 13 of a part rotatingabout an axis. The respective measurement systems are based on differentphysical effects. Angular velocity is one synonym for the rotation speedto be measured. For a mechanical gyroscopic device, the rotation to bemeasured creates a moment that is proportional to the rotation speed.Translational effects on the gyroscopic device must be compensated forusing appropriate error models. In a fiber optic gyroscopic device, thedifference in the speed of propagation of light due to rotation is onemeasure of the rotation speed to be measured. The phase shift of themeasured signal with respect to a reference signal, determined by aninterference detector, is proportional to the angular velocity. In aring laser gyroscope, two light wave trains rotate around a surface inopposite directions. The rotation of the ring laser to be measuredchanges the effective ring resonator length. The resulting frequencydifference of the light frequencies of the light wave trains is ameasure of the rotation speed. Further details can be found in thearticle “Hochgenaue Kreisel und Beschleunigungssensoren” (High-PrecisionGyroscopes and Acceleration Sensors) by E. v. Hinüber, ElektronikJanuary 1996.

In the case of oscillating gyroscopes, vibrating structures, configured,for example, as tuning forks or cylindrical bodies, are made to vibrate.Acceleration sensors measure the Coriolis acceleration that depends onthe rotation to be measured as a measure of the rotation speed. Fordetails see also “Yaw rate sensor for vehicle dynamics control system”by A. Reppich, R. Willig, SAE Paper, Detroit 1995. Rotation speed sensor11 is, however, by no means restricted to the physical principlesdescribed above. Instead, the essential thing is that rotation speed 13is available as an output signal of rotation speed sensor 11.

For axle alignment, it is important to know the angle by which theindividual wheel geometries are offset with respect to one another.Signal processor 12 converts rotation speed 13 into an angle 14 byintegrating rotation speed 13 over time. For example, if rotation speedsensor 11 detects a rotation speed 13 about the X axis, it delivers therespective angle 14 indicating how far the y/z plane has rotated aboutthe x axis since the start of the integration. Normally, a translationalmotion is superimposed on the rotation. This interference component mustbe compensated through transformation differential equations. If thereis a continuous curve of rotation speed 13, integration can be performedby electronic components. For discrete values, known algorithms areavailable to determine angle 14. The time of start of integration shouldbe communicated to signal processor 12. At this time, transducer 10 isin its reference position. If transducer 10 is made up of three rotationspeed sensors 11 arranged orthogonally to one another, all threerotation speeds 13 should be integrated and compensated in the event ofa translational component. In addition to translation, the rotation ofthe earth appears as another interfering factor. Its influence on thehorizontal angle can be taken into account as a function of the timeelapsed from the start of integration and the sine of the geographiclatitude of the location of measurement. If rotation speed sensor 11 isat rest, this angle 14 caused by the rotation of the earth can bedetermined as a function of time. On the basis of this interferencedetermination, the rotation of the earth is compensated for in thefollowing measurement. Rotation speed sensor 11 calibrates itself.

The measurement signals of rotation speed sensor 11 are preferablyprocessed locally in the respective transducer 10. One alternative is toforward rotation speed 13 unprocessed to a central processing unit,which performs the integration. The respective data can be transmittedby wire, by radio or via infrared beams.

One or more transducers 10 are needed for axis alignment. Their data isprocessed by a central display and operating device.

FIG. 3 shows and exemplary embodiment of an axis alignment procedureaccording to the present invention. Transducers 10 provided for axisalignment are aligned in step 101. For this purpose, the respectivetransducer 10 is brought into alignment with reference direction 20 in aknown orientation. The coordinates of a measuring table, for example,are used as reference direction 20, as shown in FIG. 2. Transducer 10must be arranged so that the rotation axes of rotation speed sensors 11in transducer 10 are offset by a known angle with respect to therespective axes of reference direction 20. For the sake of simplicity,it shall be furthermore assumed that transducer 10 is aligned when theaxes of rotation speed sensors 11 of transducer 10 are parallel to theaxes of reference direction 20. The known offset angle obtained betweenthe axes of rotation speed sensors 11 and reference direction 20 iszero. These initial values are stored in the central processing unit,which determines the trail angle. Since only angle differences arerelevant for the trail and camber angles, it is sufficient to arrangetransducers 10 at a certain known angular offset to one another. Afteralignment of step 101, integration of the respective rotation speeds 13is started.

The transducers are then mounted on wheels 15 a, 15 b in step 102.Transducers 10 can be attached to the wheel in any desired manner; nospecial alignment is needed in respect to the wheel 15 a, 15 b to bealigned. For example, mounting devices may be provided on the wheel rimsfor this purpose. Attachment of transducers 10 via clamps or magnets isalso conceivable. No alignment to the respective wheel axle is needed.Angles 14 by which the coordinate system formed by the axes of rotationspeed sensors 11 has rotated with respect to reference direction 20since the time of start of the integration are determined by integrationof rotation speeds 13.

Then rotation axis coordinates 21 a, 21 b of wheels 15 a, 15 b,respectively, are determined in step 103. For this purpose, transducer10 determines the rotation and wobbling motion experienced by transducer10 due to the rotation of wheel 15 a, 15 b. The wheel can be lifted orrolled for this purpose. The procedure for determining the rotation axiscoordinate with lifted wheel is known as rim impact compensation anddescribed, for example, in German Patent Application No. 29 11 580. Inrim impact compensation, the vehicle is rolled through approximatelytwo-thirds of a wheel rotation at the place of measurement, such as alift platform or shop pit. Thus it becomes known by what angle therespective rotation axis coordinates 21 a, 21 b of the respective wheels15 a, 15 b deviate from the reference direction 20.

The desired angles 14 are determined and output in step 110. The angularoffset between rotation axis coordinates 21 a, 21 b and referencedirection 20 and thus also between the individual rotation axiscoordinates 21 a, 21 b is known and is sent to the central computer,which calculates the trail angle or camber angle from this value. Ifsteerable wheels 15 a, 15 b are located on rotating platforms, thecaster or steering axis inclination can also be determined. This isdescribed, for example, in “Steering geometry and caster measurement” byD. B. January, SAE Paper, Detroit 1985.

The measurement can be verified by returning previously utilizedtransducers 10 to their initial position after completion of themeasurement, as described for step 101. In the case of a correctmeasurement, angles 14 formed on transducers 10 should not significantlydiffer from zero. If considerable differences appear, this should becommunicated to the user.

A combination of the device and the method combines their specificadvantages.

Alternative embodiments aim at simplifying transducer 10.

When one of rotation speed sensors 11, whose rotation axis ishorizontal, is not used, changes in direction with respect to thissensor can be determined using a pendulum system.

Another simplification of transducer 10 using only one rotation speedsensor 11 to measure the changes in direction in the horizontal plane ispossible when transducers 10 are transported and used essentiallyvertically. For this purpose, transducers 10 are moved suspended andattached to the essentially horizontal wheel adapters so that they canoscillate in one plane in order to determine the trail angle. Such arotation speed sensor 11 with limited degrees of freedom can beimplemented, for example, using a pendulum suspended on two threads andperforming oscillations in one plane.

In another embodiment only one rotation speed sensor 11 is used to bringthe latter into a known position with respect to a basically verticalreference direction 20 in order to determine changes in direction in thevertical plane, for example, in order to determine the camber angle.

The required measurements can be basically performed sequentially, forwhich only one transducer 10 is needed. The measured value processor isinformed when a measurement on a certain wheel 15 is completed. Therotation of the earth as an interfering component must be continuouslycompensated.

What is claimed is:
 1. A device for aligning at least one axle of avehicle, comprising: at least one transducer for determining at leastone angle between a wheel of the vehicle and a reference direction, theat least one transducer including at least one rotation speed sensorhaving an output signal which is integrated.
 2. The device according toclaim 1, wherein the at least one rotation speed sensor includes threerotation speed sensors forming an orthogonal system.
 3. The deviceaccording to claim 1, wherein the reference direction is selectedindependently from the vehicle.
 4. The device according to claim 1,wherein the at least one transducer is situated in a predeterminedposition with respect to the reference direction, and wherein the atleast one transducer is mounted on a single wheel of the vehicle.
 5. Amethod for aligning at least one axle of a vehicle having at least onetransducer, comprising the steps of: (a) arranging the at least onetransducer in a predetermined position with respect to a referencedirection; (b) after step (a), mounting the at least one transducer on asingle wheel of the vehicle; and (c) determining an angle of the atleast one transducer with respect to the reference direction, the atleast one transducer including at least one rotation speed sensor havingan output signal which is integrated, the angle formed on the singlewheel being a measure of a direction of the at least one axle.
 6. Themethod according to claim 5, further comprising the step of: (d) afterstep (b), determining a relative position of rotation axis coordinatesof the single wheel with respect to the reference direction.
 7. Themethod according to claim 6, further comprising the steps of: (f) afterstep (d), repeating step (a) to obtain a further angle; and (g) if thefurther angle is substantially different from zero, determining that theangle is invalid.
 8. The method according to claim 5, further comprisingthe step of: (e) during step (c), compensating for an influence of arotation of earth.